I took a course that covered résumé writing. Some of the most common mistakes is that people don't keep it to one page and don't highlight their particular accomplishements.
Make sure to use strong action words and focus on what you did for that company.
Say you were a entered data. You could say "typed data into computer system" or you could say "processed high volume of information into database daily and consitently surpassed speed of my co-workers"
which sounds better?